Marine vessels are commonly used modes of transport for transporting cargos and passengers over bodies of water of varying distances. To this end, it is known to transport cargos and/or passengers using different types of vessel suited to the types of cargo or passenger to be transported, for example cruise ships, cargo vessels, oil tankers, and ferry boats. However, on occasions passengers on these vessels can accidentally fall overboard and in some unfortunate cases intentionally jump overboard. Such events are known as “man overboard” events.
When a person is overboard, the typical way of detecting the occurrence of such an event is by way of witnesses. However, witnesses are not always present to see the man overboard event. This can particularly be the case at night.
When a man overboard event occurs, the vessel has to turn back and try to search for and rescue the person in the water. This search and attempted rescue procedure typically has an associated financial cost as well as a time cost. These costs are particularly acute when hours or even days have to be expended before finding the person overboard. Additionally, the longer a search continues the less likely the passenger is to be found alive. Further, the time taken to detect the man overboard event accurately can impact upon the duration of the search and rescue procedure.
A number of man overboard detection systems exist. However, many such systems require passengers to wear a tag-like device, the absence of such a device from within a monitored volume surrounding the vessel being detectable by one or more monitoring units. When a man overboard event occurs, a person wearing the device enters the water but the vessel typically continues travelling, resulting in a distance between the device and the vessel developing. In such circumstances, the device rapidly falls out of range of the monitoring units aboard the vessel and so one of the monitoring units initiates an alert to the crew of the vessel indicative of the occurrence of a man overboard event. In some systems, the devices worn by passengers are configured to detect immersion in water in order to ensure the alert is triggered with minimal delay.
While such systems are useful, they have a core requirement that the tags need to be worn by passengers. Unfortunately, the tags can be removed, either accidentally or intentionally by passengers, thereby reducing the reliability of the man overboard detection system. Furthermore, tag-based systems are not typically designed to enhance safety aboard cruise ships or ferry boats; the systems are usually used aboard smaller vessels carrying a small number of passengers where a high probability of a man overboard event occurring exists, for example aboard racing yachts.
It is therefore desirable to achieve detection of man overboard events without the use of tags that need to be worn. In this respect, detection of a fall or jump from a vessel without the use of tags is complex. The detection system needs to operate in real time, because timely detection of man overboard events is very important to increasing the probability of saving lives, especially in cold water. Performance of the detection system needs to be high: an almost 100% detection rate of man overboard events is desirable, whilst the occurrence of false alarms needs to be extremely low in order to avoid execution of unnecessary search and rescue procedures.